João de Athaydes Silva Junior

Effect of 7 yr of experimental drought on vegetation dynamics and biomass storage of an eastern Amazonian rainforest

*At least one climate model predicts severe reductions of rainfall over Amazonia during this century. Long-term throughfall exclusion (TFE) experiments represent the best available means to investigate the resilience of the Amazon rainforest to such droughts. *Results are presented from a 7 yr TFE study at Caxiuanã National Forest, eastern Amazonia. We focus on the impacts of the drought on tree mortality, wood production and above-ground biomass. *Tree mortality in the TFE plot over the experimental period was 2.5% yr(-1), compared with 1.25% yr(-1) in a nearby control plot experiencing normal rainfall. Differences in stem mortality between plots were greatest in the largest (> 40 cm diameter at breast height (dbh)) size class (4.1% yr(-1) in the TFE and 1.4% yr(-1) in the control). Wood production in the TFE plot was c. 30% lower than in the control plot. Together, these changes resulted in a loss of 37.8 +/- 2.0 Mg carbon (C) ha(-1) in the TFE plot (2002-2008), compared with no change in the control. *These results are remarkably consistent with those from another TFE (at Tapajós National Forest), suggesting that eastern Amazonian forests may respond to prolonged drought in a predictable manner.

Ecosystem respiration and net primary productivity after 8–10 years of experimental through-fall reduction in an eastern Amazon forest

Background: There is much interest in how the Amazon rainforest may respond to future rainfall reduction. However, there are relatively few ecosystem-scale studies to inform this debate. Aims: We described the carbon cycle in a 1 ha rainforest plot subjected to 8–10 consecutive years of ca. 50% through-fall reduction (TFR) and compare these results with those from a nearby, unmodified control plot in eastern Amazonia. Methods: We quantified the components of net primary productivity (NPP), autotrophic (R a) and heterotrophic respiration, and estimate gross primary productivity (GPP, the sum of NPP and R a) and carbon-use efficiency (CUE, the ratio of NPP/GPP). Results: The TFR forest exhibited slightly lower NPP but slightly higher R a, such that forest CUE was 0.29 ± 0.04 on the control plot but 0.25 ± 0.03 on the TFR plot. Compared with four years earlier, TFR plot leaf area index and small tree growth recovered and soil heterotrophic respiration had risen. Conclusions: This analysis tested and extended the key findings of a similar analysis 4 years earlier in the TFR treatment. The results indicated that, while the forest recovered from extended drought in some respects, it maintained higher overall R a relative to the undroughted control, potentially causing the droughted forest to act as a net source of CO2.

Variabilidade espacial do conforto térmico e a segregação social do espaço urbano na cidade de Belém, PA

O presente trabalho vem contribuir com o estudo do clima urbano na cidade de Belem durante a epoca menos chuvosa, juntamente com uma analise das questoes da segregacao social deste espaco urbano. Foi realizada uma campanha de coleta de dados meteorologicos durante alguns dias na epoca menos chuvosa da regiao para se calcular o indice de conforto termico nos bairros e compara-los com as tipologias sociais caracteristicas de cada bairro. Os resultados indicaram que as zonas da cidade menos confortaveis foram a Oeste e a Central, pois sao mais urbanizadas e possuem menos vegetacao que as demais areas, enquanto que as zonas mais confortaveis foram a Leste e Noroeste, que possuem mais areas vegetadas e predominância de edificacoes baixas. As analises indicaram que nao existe um padrao bem definido entre as tipologias sociais dos bairros e suas condicoes de conforto termico, pois as caracteristicas da superficie sao mais significativas para as mudancas microclimaticas locais.

Variabilidade sazonal da condutância estomática em um ecossistema de manguezal amazônico e suas relações com variáveis meteorológicas

) para o periodo chuvoso (marco) e seco (agosto) do ano de 2003, e suas relacoes de dependencia com algumas variaveis meteorologicas medidas em um ecossistema de manguezal amazonico. As informacoes utilizadas foram do projeto ECOBIOMA, parte integrante do Experimento de Grande Escala da Biosfera-Atmosfera da Amazonia (LBA). A g

Fluxos de CO2 do solo na floresta nacional de Caxiuanã, Pará, durante o experimento ESECAFLOR/LBA

The ESECAFLOR/LBA experiment was carried out at the Caxiuana National Forest, Para State, and this article intends to investigate the effect of hydrological stress on the total soil respiration. Two adjacent 1 hectare plots were defined in January 2002. One plot remained in its natural conditions and was used as a control (A), while in the exclusion plot (B) plastic cover panels were installed in order to drain about 70% of the total rainfall to outside of the plot. Accumulated monthly rainfall was recorded from 2005 January to December. During 2005 the rainfall over the ECFPn was 2,211.6 mm, or 9.96% above the mean of 2,011.2 mm. The average soil moisture was 15.6±9.2 and 9.5±3.4% in the plots A and B, respectively. The average soil temperature was 25.6±0.4 and 25.7±0.5 oC, for the A and B plots, respectively. The average soil CO2 flux was 3.46±0.44 and 3.21±0.84 μmolCO2 m-2s-1 in the A and B plots, respectively. With the exclusion of part of rain in plot B, it had a reduction of 7.23% in the soil CO2 flux (0.25 μmolCO2 m-2s-1), 39.1% in the soil humidity (6.1p.p.), and an increase of 0.39% in the soil temperature (0.1oC). The soil moisture in parcel B was lesser than in the parcel A, due to the exclusion system of rain. However at the beginning of the year, site B undergone some changes causing the measuring values to be about the same on both areas.

Drought stress and tree size determine stem CO2 efflux in a tropical forest.

Summary CO 2 efflux from stems (CO 2_stem) accounts for a substantial fraction of tropical forest gross primary productivity, but the climate sensitivity of this flux remains poorly understood. We present a study of tropical forest CO 2_stem from 215 trees across wet and dry seasons, at the worlds longest running tropical forest drought experiment site. We show a 27% increase in wet season CO 2_stem in the droughted forest relative to a control forest. This was driven by increasing CO 2_stem in trees 10–40 cm diameter. Furthermore, we show that drought increases the proportion of maintenance to growth respiration in trees > 20 cm diameter, including large increases in maintenance respiration in the largest droughted trees, > 40 cm diameter. However, we found no clear taxonomic influence on CO 2_stem and were unable to accurately predict how drought sensitivity altered ecosystem scale CO 2_stem, due to substantial uncertainty introduced by contrasting methods previously employed to scale CO 2_stem fluxes. Our findings indicate that under future scenarios of elevated drought, increases in CO 2_stem may augment carbon losses, weakening or potentially reversing the tropical forest carbon sink. However, due to substantial uncertainties in scaling CO 2_stem fluxes, stand‐scale future estimates of changes in stem CO 2 emissions remain highly uncertain.

Thermo- hygrometric variations and study of urban heat island in the city of Bragança -PA and surrounding region

Revista Brasileira de Geografia Física, vol. 9, n. 02, (2016) 571-584. 572 Costa e Costa, A., Rodrigues, H. J. B., Costa, J. L. O., Souza, P. F. de S., Silva Junior, J. A., Costa, A. C. L. night, thus causing certain human discomfort. With that, the microclimate changes in the city of Bragança-PA, as well as other urban centers in general are caused by human activities that interfere with peoples quality of life. This work is important for publication in the magazine due to their scientific contribution to society

VARIAÇÃO SAZONAL DA POPULAÇÃO DE BACTÉRIAS E FUNGOS E DOS TEORES DE NITRATO E AMÔNIO DO SOLO NOS SÍTIOS DO LBA E PPBIO, NA AMAZÔNIA ORIENTAL

E possivel que os fatores ambientais, que determinam o comportamento da microbiota edafica, estejam sendo modificados pelas mudancas climaticas de origem natural e/ou antropica. A fim de verificar o efeito da exclusao de agua sobre a populacao de bacterias e fungos do solo, foi desenvolvido o presente estudo na area do experimento ESECAFLOR, que simula a ocorrencia de fenomenos extremos, como o evento El Nino, e na area do Programa de Pesquisa em Biodiversidade - PPBio (Floresta Primaria), que visa estudar a Biodiversidade da Amazonia, sendo esta usada como controle para fins comparativos. As amostras de solo foram coletadas nas profundidades: 0-5, 5-10, 10-20 e 20-30 cm, nos periodos sazonais chuvoso, de transicao e menos chuvoso. Os maiores valores de Unidades Formadoras de Colonias (UFC) para as populacoes de Bacterias e Fungos foram 196 x 104 UFC/g de solo e 124 x 102 UFC/g de solo, respectivamente, ambos na area sem intervencao antropica (PPBio). A umidade do solo e a variavel que teve maior influencia nos valores nas contagens obtidas das populacoes de fungos e bacterias.

Análises do Conforto Térmico em uma cidade de grande porte na Região Amazônica: O Caso de Belém, Pará

As pesquisas sobre o conforto termico surgiram devido as preocupacoes com a melhoria das condicoes de trabalho e da qualidade de vida da populacao. Neste estudo analisaram-se as condicoes de conforto termico a qual a populacao da cidade de Belem esta submetida, atraves de medidas de campo e aplicacao do Indice de Calor (IC). Os resultados encontrados apontaram que a maior parte do periodo diurno a cidade e desconfortavel termicamente, com base nos valores encontrados do IC. Os bairros com maior porcentagem de impermeabilizacao do solo e menos cobertura vegetal apresentou maior desconforto termico, indicando que os elementos urbanos contribuem para o clima da cidade.